BIonic membranes and AdS instabilities

Abstract

We study 4d membranes in type IIA flux compactifications of the form AdS4× X6, where X6 admits a Calabi-Yau metric. These models feature scale separation and D6-branes/O6-planes on three-cycles of X6. When the latter are treated as localised sources, explicit solutions to the 10d equations of motion and Bianchi identities are known in 4d N = 1 settings, valid at first order in an expansion parameter related to the AdS4 cosmological constant. We extend such solutions to a family of perturbatively stable N = 0 vacua, and analyse their non-perturbative stability by looking at 4d membranes. Up to the accuracy of the solution, we find that either D4-branes or anti-D4-branes on holomorphic curves feel no force in both N = 1 and N = 0 AdS4. Differently, D8-branes wrapping X6 and with D6-branes ending on them can be superextremal 4d membranes attracted towards the N = 0 AdS4 boundary. The sources of imbalance are the curvature of X6 and the D8/D6 BIon profile, with both comparable terms as can be checked for X6 a (blown-up) toroidal orbifold. We then show that simple N = 0 vacua with space-time filling D6-branes are unstable against bubble nucleation, decaying to N = 0 vacua with less D6-branes and larger Romans mass.